1. Field of the Invention
The present invention relates to an improvement in a control system for a choke valve of a carburetor, including a choke-operating lever for opening and closing the choke valve of the carburetor, a choke spring for biasing the valve in an opening direction, and a damper for controlling the opening motion to a lower speed, when the choke valve is opened from its fully closed position by a biasing force of the choke spring. The choke-operating lever, the choke spring and the damper are connected to the choke valve of the carburetor, so that after starting of an engine with the choke valve closed, the choke valve is opened automatically in response to the progress of the warming operation of the engine, thereby providing the stabilization of the warming operation and a reduction in fuel consumption.
2. Description of the Related Art
In a conventional control system for the choke valve of the carburetor, the damper an air type in which the opening motion of the choke valve is slowed down by a damping force generated upon passing of air through an orifice (see Japanese Utility Model Application Laid-open No. 63-24354.
For providing the stabilization of the warming operation and a reduction in fuel consumption, it is important that the time required from the full closing to the full opening of the choke valve after starting of the engine is controlled in accordance with the level of the environmental temperature of the engine. Namely, it is necessary to provide the choke valve control system with the characteristic that the lower the environmental temperature, the longer the required time for the valve to go from fully closed to fully open.
In the control system for the choke valve of the carburetor using the air damper, as described above, however, the damping force generated in the air damper is constant irrespective of the level of the environmental temperature of the engine and hence, the time required for fully opening the choke valve controlled by the control system is also constant. Thus, it is impossible to satisfy the above-described required characteristic.
Accordingly, it is an object of the present invention to provide a control system for a choke valve of a carburetor, which is designed so that the above-described required characteristic can be satisfied.
To achieve the above object, according to the present invention, there is provided a control system for a choke valve of a carburetor, comprising a choke-operating lever for opening and closing the choke valve of the carburetor, a choke spring for biasing the valve in an opening direction, and a damper for controlling opening motion of the choke valve to a lower speed, when the choke valve is opened from its fully closed position by a biasing force of the choke spring, the choke-operating lever, the choke spring and the damper being connected to the choke valve of the carburetor, wherein the damper is an oil type using a damper oil whose viscosity is increased in accordance with a temperature drop or decrease.
With the first feature, a damping force generated by the oil damper is increased in accordance with the decrease of the environmental temperature of the engine. Therefore, the time required from the full closing to the full opening of the choke valve can be controlled, so that the time is longer when the environmental temperature is lower, and the time is shorter when the environmental temperature is higher. Thus, it is possible to satisfy the easy/ready startability of the engine, the stabilization of the warming operation of the engine and a low fuel consumption.
According to a second feature of the present invention, in addition to the first feature, the damper comprises a damper housing, a rotor rotatably housed in the damper housing, and the damper oil accommodated in a sealed manner in the damper housing and applying a viscosity resistance to the rotation of the rotor, the damper housing being supported on a stationary structure, and the rotor being connected to the choke valve so that the rotor is rotated in operable association with the opening and closing of the choke valve.
With the second feature, the damper can be constructed compactly by a small number of parts, which can contribute to a reduction in cost of and the compactness of the choke control system.
The stationary structure corresponds to a bracket 14 in each of embodiments of the present invention which will be described hereinafter.
According to a third feature of the present invention, in addition to the first or second feature, a driven member is connected to a valve stem of the choke valve, and a resilient driving member is connected to the choke-operating lever and adapted to be flexed to urge one side of the driven member in operable association with the operation of the choke-operating lever in a direction of closing of the choke valve, thereby closing the choke valve.
With the third feature, fabrication errors of various portions of the choke valve control system are absorbed by the flexing of the resilient driving member, and the choke valve can be brought reliably and at any time into the fully closed state.
The driven member and the resilient driving member correspond to a driven pin and a resilient driving plate 47 in each of the embodiments of the present invention which will be described hereinafter.
According to a fourth feature of the present invention, in addition to the second feature, a cam adapted to be rotated in operable association with the opening and closing operation of the choke-operating lever, and a cam follower adapted to be moved following a cam surface of the cam to open and close the choke valve are interposed between the choke-operating lever and the choke valve.
With the fourth feature, after starting of the engine with the choke valve fully closed, the time required for fully opening the choke valve is controlled by the damper, E and the opening degree of the choke valve during such controlling is controlled by the cam surface. Therefore, a desired opening degree characteristic assuring that the fully closed state is maintained, can be provided to the choke valve during the passage of time by the selection of the shape of the cam surface, thereby providing the stabilization of the warming operation and an enhancement in low fuel consumption.
According to a fifth feature of the present invention, in addition to the first feature, the damper comprises a damper housing and the damper oil accommodated in a sealed manner in the damper housing and applying a viscosity resistance to the rotation of a rotor, the damper housing being supported on a stationary structure, and wherein the rotor and the cam are connected to each other through an accelerating mechanism for accelerating the rotation of the cam to transmit it to the rotor.
With the fifth feature, a damping force generated by the damper is increased in accordance with a drop or decrease of the environmental temperature of the engine. Therefore, the time required for fully opening the choke valve can be controlled automatically, so that the time is longer when the environmental temperature is lower, and the time is shorter when the environmental temperature is higher. Thus, it is possible to satisfy the easy/ready startability of the engine, the stability of the warming operation of the engine and a low fuel consumption.
Moreover, the damper can generate sufficient damping force, although the damper is compact, by transmitting the rotation of the cam to the rotor of the damper through the accelerating mechanism and thus, it is possible to provide a satisfactory time required for fully opening the choke valve.
According to a sixth feature of the present invention, in addition to the first feature, the damper comprises a damper housing, a rotor rotatably housed in the damper housing and the damper oil which is accommodated in a sealed manner in the damper housing and whose viscosity is increased in accordance with a temperature drop to apply a viscosity resistance to the relative rotation of the rotor and the damper housing, one of the damper housing and the rotor being secured to a stationary structure, the choke-operating lever being integrally connected to the other of the damper housing and the rotor, and wherein a return spring for biasing the choke-operating lever in a direction to open the choke valve is connected to the choke-operating lever.
With the sixth feature, a damping force generated by the oil-type damper is increased in accordance with a decrease of the environmental temperature of the engine. Therefore, the time required from the full closing to the full opening of the choke valve can be controlled automatically, so that the time is longer when the environmental temperature is lower, and the time is shorter when the environmental temperature is higher. Thus, it is possible to satisfy the easy/ready startability of the engine, the stability of the warming operation of the engine and a low fuel consumption.
In addition, the oil-type damper comprising the damper housing, the rotor and the damper oil is constructed by a small number of parts to be compact. Moreover, it is possible to reduce the number of parts of the choke valve control system by the integral connection of any one of the damper housing and the rotor with the choke-operating lever, to thereby simplify the structure to provide the compactness and reduce the cost of the choke valve control system.
According to a seventh feature of the present invention, in addition to the sixth feature, the choke-operating lever is provided with a cam which is engaged with a cam follower supported on the stationary structure and operably connected to the choke valve, the cam being formed so that the motion of the choke-operating lever for opening the choke valve is transmitted through the cam follower to the choke valve in a retarded manner.
With the seventh feature, even if the turning speed of the choke-operating lever in the direction to open the choke valve, which is determined by the damping force of the oil damper and the return spring, is constant, the opening of the choke valve can be retarded as desired by the shape of the cam to provide the easy/ready startability of the engine and the stabilization of the warming operation of the engine.
According to an eighth feature of the present invention, in addition to the first feature, a cam adapted to be rotated in operable association with the opening and closing operation of the choke-operating lever and a cam follower adapted to be moved following a cam surface of the cam to open and close the choke valve are interposed between the choke-operating lever and the choke valve.
According to a ninth feature of the present invention, in addition to the eighth feature, the damper comprises a damper housing, and the damper oil which is accommodated in a sealed manner in the damper housing and applies a viscosity resistance to the rotation of a rotor, the damper housing being supported on a stationary structure, and wherein the rotor and the cam are connected to each other through an accelerating mechanism for accelerating the rotation of the cam to transmit it to the rotor.
According to a tenth feature of the present invention, there is provided a control system for a choke valve of a carburetor in a power working machine including an engine which has a cooling fan mounted at an upper end of a crankshaft disposed vertically, a working device connected to a lower end of the crankshaft, and an engine cover which has a cooling-air intake port opposed to the cooling fan and covers an upper surface of the engine so that cooling air drawn through the cooling-air intake port by the cooling fan is guided to the engine, the control system comprising: a choke-operating lever for opening and closing a choke valve of a carburetor mounted on one side of the engine; a choke spring for biasing the choke valve in an opening direction; and a damper for controlling the motion of opening of the choke valve to a lower speed, when the choke valve is opened from its fully closed position by a biasing force of the choke spring, wherein the damper an oil type using an damper oil whose viscosity is increased in accordance with a temperature decrease.
According to an eleventh feature of the present invention, in addition to the tenth feature, the damper is disposed in a path for the cooling air extending from the cooling-air intake port to the engine.
With the eleventh feature, the cooling air drawn through the cooling-air intake port in the engine cover by the cooling fan during operation of the engine is passed through the damper and around the damper in a course of being fed under pressure to the engine, whereby it blows away dusts deposited on the damper and parts of the choke valve control system connected to the damper to clean them. Therefore, it is possible to prevent the dusts blown up by the working device from being accumulated on the damper and the like, thereby also preventing any associated malfunction of the damper and the like, and cooling the damper to enhance the durability thereof.
According to a twelfth feature of the present invention, in addition to the tenth feature, a tip end of the choke-operating lever is disposed to protrude outside of the engine cover.
With the twelfth feature, the choke-operating lever can be opened and closed easily without being obstructed by the engine cover. Moreover, the choke-operating lever can be visually seen and hence, it is easy to confirm the position of the choke-operating lever and it is possible to easily carry out the appropriate control of the choke valve.
According to a thirteenth feature of the present invention, in addition to the tenth feature, the power working machine further includes a braking mechanism capable of braking the rotation of an output shaft of the engine, and a brake release mounted on a steering handle bar for releasing the operational state of the braking mechanism; the choke-operating lever, the choke spring and the damper are connected to the choke valve; the choke-operating lever is adapted to be turned between an opening position and a closing position to open and close the choke valve; and a locking mechanism is interposed between the choke-operating lever and the braking mechanism and adapted to lock the choke-operating lever at the closing position when the braking mechanism is in operation, and to release the locked state of the choke-operating lever when the operation of the braking mechanism is released.
With the thirteenth feature, when the operation of the braking mechanism is released, the locked state of the choke-operating lever is released automatically in operable association with the releasing of the operation of the braking mechanism, and the closing of the choke valve is controlled automatically to a lower speed. Therefore, a special operation for returning the choke-operating lever is not required and thus, it is possible to alleviate a burden on an operator, and also to prevent the malfunction of the engine and the degradation of the fuel consumption due to the operator forgetting to open the choke valve.
According to a fourteenth feature of the present invention, in addition to the thirteenth feature, the damper is comprised of a damper housing, a rotor rotatably housed in the damper housing and the damper oil accommodated in a sealed manner in the damper housing and applying a viscosity resistance to the rotation of a rotor, the damper housing being supported on a stationary structure, and wherein the rotor and a cam operatively associated with the choke-operating lever and the choke valve are connected to each other through an accelerating mechanism for accelerating the rotation of the cam to transmit it to the rotor.
With the fourteenth feature, a damping force generated by the damper is increased in accordance with the decrease of the environmental temperature of the engine. Therefore, the time required for the full opening of the choke valve can be controlled, so that the time is longer when the environmental temperature is lower, and the time is shorter when the environmental temperature is higher. Thus, it is possible to satisfy the easy/ready startability of the engine, the stabilization of the warming operation of the engine and a low fuel consumption.
Moreover, the damper can generate a sufficient damping force although the damper is compact, thereby providing a satisfactory time required for the full opening of the choke valve, by transmitting the rotation of the cam through the accelerating mechanism to the rotor of the damper.
The above and other objects, features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.